Hello, I Am 55 Yr Old Female, I Have Gained

Hello, I am 55 yr old female, I have gained 30 pounds, trouble eating regular meals, I get so very full on small amounts of food I eat, going to bathroom more often and having a 2 phase test done to see where and if the food I eat is going to intestine properly, yesterday did the oatmeal, they had me eat oatmeal to see how long it takes the food to get going and most of it sat there in my upper stomach. Monday I go for the fluid drinking to see how fast it will travel and where. But I feel full all the time and can only eat when my stomach tells me it is ready to eat a small meal. Lately have been only able to eat 1 meal a day. Have any idea why this is happening or what can cause this. I feel it's not good at all, can't be when I am not eating not even 2 meals a day and have gained from 145 pds to 173 pds, though I did stop smoking last Nov 2014. Can you answer anything for me please? Sherry